Laser-induced breakdown spectroscopy (LIBS) is a kind of rapid component analysis technique. Basic principle of the LIBS technique is to focus a high-energy laser beam on surface of a to-be-measured sample so as to generating plasma by ablating, and then to obtain different types of elements of the sample and content thereof by analyzing plasma emission spectrum. Several unique advantages of the LIBS technique, such as simultaneous analysis of multiple elements, no sample preparation, in-situ detection, fast and remote detection and so on, make the technique continuously become a research hotspot, and be preliminarily applied in industries.
After fifty years' development, qualitative analysis of the LIBS technique has been widely recognized. However, analytical accuracy of the LIBS technique is lower than that of a conventional component analysis technique. At present, qualitative analysis has become an important and difficult research issue in the LIBS technique. As the LIBS technique employs laser as an excitation source, complexity of interaction between the laser and materials results in un-uniformity of temporal and spatial distribution of laser plasma, as well as light emission from particles in an excited state at the center of the laser plasma. As the light passes an outer layer, it is absorbed by particles in a ground-state of elements on the outer layer of the same type, and central intensity of a spectral line thereof is decreased and deformed, which is referred to as self-absorption effect. The self-absorption effect significantly affects emission light of the laser plasma, which causes quantitative accuracy of the LIBS technique to be poor. Therefore, negative effect of the self-absorption effect has to be eliminated so as to ensure accurate quantitative analysis of the LIBS technique.
Conventionally, there are two methods for weakening self-absorption effect of the laser plasma, the first one is to establish self-absorption mathematical models for correcting spectrum affected by self-absorption by processing experimental data and analyzing self-absorption effect of spectral lines; however, due to complexity of laser-induced plasma, the model can only correct part of self-absorption in spectrum, and thus this kind of methods has great limitation; the second one is to use special experimental environment or devices, and comprises changing a type of ambient gas, air pressure, spatial constraint of reflective mirrors and so on; but this kind of method can only be applicable for element detection under special conditions, which sacrifices fast detection of the LIBS technique in atmospheric environment useless.